Field of the Invention
The embodiments described herein are generally directed to a regional positioning system, and, more particularly, to transmit-and-response range-finding.
Description of the Related Art
There have been prior attempts to create a high-precision indoor positioning system. While a few have been functional, none have become widespread or economical. With the advent of Bluetooth™ LE and iBeacon™ technology, it was assumed that indoor tracking systems would become commonplace. Some have claimed that iBeacon™ can be used to implement an indoor tracking system similar to the Global Positioning System (GPS). Unfortunately, the technique used by iBeacon™ is not capable of this type of resolution and triangulation.
Conventionally, there are three techniques employed for determining the position of a target within a region. All three techniques require placing one or more beacons in known locations:                (1) Use signal strength to determine the distance of a target relative to a beacon of known location. This is the technique currently used by iBeacon™. Unfortunately, signal strength can vary greatly, depending on the objects (e.g., people, electronics, furniture, plants, etc.) around and between the beacon and the target. As a result, the target can only determine a rough range to the beacon (immediate 0-0.3 m, low 0.4-2 m, and high greater than 2 m). In addition, these rough ranges are not guaranteed due to unknown fluctuations in the signal strength received by the target.        (2) Reflect a signal off of a target, and use the length of time for the signal to reach the target and return to determine the distance of the target. This is the technique used by radar and laser range finders. It has the advantage of being very accurate and not requiring all devices' clocks to be synchronized. However, it has the disadvantage of requiring the target to be within a line of sight of the range-finding device.        (3) Synchronize the clocks of all devices, with beacons at known locations sending a signal at regular intervals, and determine a target's position using the arrival times of these signals. This is the technique used by GPS. It has the advantage of being very accurate and able to operate with an unlimited number of targets without using additional bandwidth. However, it has the disadvantage of requiring the clocks of all of the beacons to be highly synchronized.        
There have been a number of devices created using the second and third techniques in their pure form (e.g., radar guns, handheld GPS devices). However, all of these devices are unsuitable for use in an indoor positioning system.